Lithotripters for use in the extracorporeal destruction of kidney stones have become well known. Such devices use a reflector that is a portion of an ellipsoid. A spark generating device is positioned at the first focus point of the ellipsoid, while the ellipsoid is truncated so that the second focus point can be located precisely on the kidney stone, gallstone, or other concretion to be disintegrated. As is known, the reflector is filled with water, and is coupled to the body containing the concretion that is to be disintegrated. The spark gap previously noted has a series of sparks jump across it under water. This causes flashing of some of the water into steam, some dissociation of the water, and generally creates a shockwave which is reflected by the truncated ellipsoidal reflector. The shockwave passes through the water in the reflector and through the human body, which is mostly water and focuses on the stone which in due course is reduced to dust which passes out with the urine. The process is also useful in destroying concretions in the gall bladder.
The first focus point is relatively easily located, either by calculations, or by the predetermined position of the spark gap. However, it is difficult to ascertain simply and with accuracy the location of the second focus point. Furthermore, it is difficult to test the ellipsoidal reflector surface to make sure that it is substantially perfect, and within tolerances.